This invention relates to the bonding of a small object, such as a transducer or an identification label, precisely and reliably to a component for the purpose of measurement or identification, and more specifically, to the bonding of an ultrasonic transducer to a fastener to produce a load indicating fastener using a process which is both easy and reliable for a technician in a test lab or at an assembly or construction site.
For some time, ultrasonics has been used to accurately measure the load in bolts. Initially, removable ultrasonic devices were the most commonly used. More recently, low-cost permanent ultrasonic transducers, which can be permanently attached to one end of the fastener, have come to be used. Permanent fasteners of this type are described, for example, in U.S. Pat. No. 4,846,001 (Kibblewhite), issued Jul. 11, 1989; U.S. Pat. No. 5,131,276 (Kibblewhite), issued Jul. 21, 1992; U.S. Pat. No. 6,990,866 (Kibblewhite), issued Jan. 31, 2006; and U.S. Pat. No. 8,028,585 (Kibblewhite) issued Oct. 4, 2011, the subject matter of each of which is incorporated by reference as if fully set forth herein.
Load measurements in fasteners using ultrasonics use a pulse-echo technique to determine the time-of-flight or acoustic length of the fastener. With permanently attached transducers that are bonded to an end of a fastener with an adhesive, such measurements are very dependent on the position of the transducer and the characteristics of the bond. In addition to providing the mechanical attachment, the adhesive acts as an acoustic couplant and an electrical capacitive coupling to the bolt surface. In order for the ultrasonic transducer to transmit and receive the acoustic waves effectively, the adhesive layer or “bond line” must be thin and free of air bubbles. In order to measure load accurately, the transducer must be precisely centered relative to the bolt shank on the end surface to minimize the effect of variations in stress across the diameter of the shank. Since this thin, repeatable bond line is difficult to achieve, the most accurate permanent ultrasonic transducer load indicating fasteners, such as i-Bolt® fasteners manufactured by Load Control Technologies of King of Prussia, Pa., are bonded in a manufacturing facility with precision automated robotic equipment.
There is a need for producing load indicating fasteners quickly for urgent test and development programs and, consequently, ultrasonic load measurement equipment manufacturers provide ultrasonic transducers for bonding to fasteners by the user to make load indicating fasteners.
An example of such an ultrasonic transducer and attachment procedure is described in the operating manual for the MC900 Transient Recorder manufactured by MicroControl, Inc. of Troy, Mich., the subject matter of which is incorporated by reference as if fully set forth herein. However, these manual manufacturing processes lack an effective way to precisely position the transducer and the operation is difficult and time consuming. Furthermore, poor bond line repeatability can cause measurement unreliability and inaccuracies.
It therefore remains desirable to provide a system which allows a user to make load indicating fasteners easily and quickly while achieving the precise placement and bond integrity of factory produced load indicating fasteners, and to provide a practical technique for applying a transducer to an already installed fastener, or in other situations in which the fastener cannot be oriented with its bonding surface facing up.